passing large quantities of current through the cells, this will prove fully as disastrous as discharging the battery too rapidly. The manufacturers of various batteries recommend a certain normal charging rate, as well as a discharge rate.

A battery must a ways be charged longer than its rated capacity would indicate. For instance, if a charging rate of 5 amperes was recommended and a battery of 60 ampere hour capacity was to be restored to activity, it would take about 15 or 16 hours to charge it instead of the 12 hours one might think necessary if the total

capacity was divided by the charging rate. Storage batteries can be charged directly from 110 volt or 220 volt direct current lighting circuits by simply using a bank of lamps in series with the battery as indicated at Fig. 93 or a rheostat as shown at Fig. 93-A to regulate the number of amperes flowing into the battery. Then a bank of lamps is employed, either 16, 32 or 64 candle power bulbs may be utilized. A 16 candle power carbon filament lamp consumes about .5 of an ampere when used on 110 volt circuit. If it is desired to pass 3 amperes of current through the battery one can use six 16 candle power lamps in multiple or three 32 candle power; or one 64

and one 32 candle power bulb. When a rheostat is used an ammeter is interposed in the circuit in order to determine the amount of current flowing through the battery. The amperage can be regulated by varying the position of the rheostat control handle so that more or less resistance is interposed in the circuit.

Q. How are storage batteries charged from alternating current?

A. Storage batteries can be charged from alternating current only by using some form of rectifier in order that the alternating impulses will be made to flow through the battery in only one direction. These may be of the mercury bulb or electrolytic form, both types having been used with success.

Q. What is the electrolyte of the storage battery?

A. The electrolyte or exciting liquid used in a storage battery is a dilute solution of sulphuric acid and water, mixed to the proportion of about ten parts water to one part acid.

Q. What is its specific gravity when battery is fully charged, and how is this determined?

A. The specific gravity of the electrolyte forms a good indication of the condition of the storage battery. When fully charged, the specific gravity should be 1350 degrees when tested with the standard form of hydrometer, having suitable scale for use with storage battery electrolyte.

Q. How does a mechanical generator of electricity produce current?

A. The current of electricity obtained from a mechanical generator is derived by passing a number of loops of wire wound around a soft iron core between the pole pieces of a powerful magnet so these coils of wire cut the lines of magnetic force. This induces a current of electricity in them proportional to the speed at which they are rotated, the number and size of the coil loops and the strength of the magnetic energizing field.

Q. What is the difference between a dynamo and magneto? A. A dynamo differs from a magneto principally in the manner of creating a magnetic field. In the dynamo electro-magnets are

used to excite the pole pieces between which the armature revolves, while in the magneto the field magnets are of the permanently excited type without any winding.

Q. Describe action of typical dynamo.

A. A typical dynamo is shown in section at Fig. 94. The principal parts are the armature, which revolves between the pole pieces, and the field magnet which surrounds the armature. A large number of windings of insulated wire are suitably disposed on the armature core and are connected to segments of a collecting device termed a "commutator," which is mounted on the armature shaft so that it turns with the armature. The shaft to which the armature and commutator are secured is mounted on ball bearings and is driven by

a friction governor which prevents the armature from being driven at excessive speeds. The field magnets are composed of a number of stamped laminæ of soft iron around which are wound two coils of wire that serve to magnetize the field when a current of electricity is passed through them. As the armature is revolved between the pole pieces, the electrical current induced in the armature windings is delivered to the commutator, from which it is collected by brushes attached to terminals by which the device is joined to the external circuit. The entire assembly is housed in a metal case so it is completely protected.

Q. How many types of magneto are used?

Two main forms of magneto are used for motor car ignition

purposes. One of these generates a current of low voltage and is called a "low tension magneto," while the other form produces current of high potential and is called a "high tension magneto." Q. Describe action of low tension device.

A. The low tension magneto has an armature winding composed of but one size of wire, and before the current will overcome the resistance of the air gap at the spark plug points it must be transformed to a higher voltage by means of an induction coil.

Q. How does high tension magneto differ in construction from low tension types?

A. There is no marked difference in general design of high and low tension magnetos. The difference is principally in the armature winding, which is a double form on the high tension device. A current of sufficiently high potential is delivered directly from the armature to the spark plug in the high tension system because the two windings give practically the same effect as is obtained from the ordinary form of induction coil.

Q. What are the advantages of the true high tension principle?

A. The high tension magneto has advantages that are readily perceived. Owing to the elimination of the induction coil and its auxiliary wiring it is a self contained device that is practically a complete ignition system in itself, needing only spark plugs in the cylinders and short wires connecting them to the distributor of the magneto to complete it.

Q. Wherein is a dynamo superior to a magneto?

A. A dynamo is superior to a magneto in all cases where currents of large amperage and constant value are needed, as in charging storage batteries or supplying current for electric lights and electric self-starting systems.

Q. Why is a magneto better for ignition?

A. A magneto is superior for ignition because on the efficient forms they will produce a current of sufficient intensity to explode the gas charge in the cylinders when turned at very low speed. The usual form of high tension magneto will produce a hot spark with but a quarter turn of the armature, which makes it possible to